Rotating machines are commonly used to drive rotational loads such as pump impellers. In certain applications, the process fluid pumped by the impeller is not compatible with elements of the rotating machine. In such applications, the rotating machine must be isolated from the process fluid. Otherwise, the elements of the rotating machine must be constructed of materials compatible with the fluid. This specification describes a rotating machine adapted for use in an electro-hydraulic power steering unit, however other applications are contemplated.
In typical power steering pump designs, the motor drive has two endshields and uses ball bearings to reduce friction generated by rotation of the shaft. The motor is generally separated from the fluid by a seal on the shaft. The use of a ball bearing motor in the presence of hydraulic fluid limits the life expectancy of the ball bearings. Leakage of the hydraulic fluid past the shaft seal will contaminate the bearing lubricant, leading to the eventual demise of the ball bearings. It is therefore desirable for a rotating machine adapted for use in a pump application to be compatible with the process fluid being pumped. It s further desirable for a rotating machine adapted for use in a pump application to be capable of being immersed in the process fluid, thus obviating the need for a seal between the rotating machine and the pump.
In rotating machines using permanent magnet motors, it is common to attach permanent magnets on a rotor member to form a rotor assembly. The permanent magnets may be attached by retaining members or adhesives. In the process of attaching the magnets, the thickness and uniformity of the adhesive layer greatly determines the shear strength of the adhesive. It is desirable to control the thickness and uniformity of the adhesive layer to ensure adequate adhesion. It is also desirable to provide a back-up retention means should the adhesive layer fail.
Another important aspect in the assembly of a rotating machine lies in assuring alignment between the stator of the machine and the position sensors used to indicate the relative position of the rotor during operation and control of the machine. Typically Hall effect sensors are placed near the rotor to sense magnetic field changes caused by the interaction between the magnets on the rotor and the stator poles, thus allowing the control electronics to time the switching on and off of the phase windings to control machine torque and speed. The alignment of the sensors relative the stator is crucial to this timing process. Typically, the sensors are adjusted after fabrication of the rotating machine to ensure the proper timing. It is desirable for a rotating machine to have features which align the stator poles relative to the position sensors during the assembly process, thus obviating the need for further adjustment after assembly has been completed.